Protein-Rich Diet Boosts the Benefit of Exercise

"There's an additive, interactive effect when a protein-rich diet is combined with exercise. The two work together to correct body composition; dieters lose more weight, and they lose fat, not muscle," said Donald Layman, a U of I professor of food science and human nutrition.

A higher-carbohydrate, lower-protein diet based on the USDA food guide pyramid actually reduced the effectiveness of exercise, Layman said.

Forty-eight adult women participated in Layman's 4-month study. One group ate a protein-rich diet designed to contain specific levels of leucine, one of the essential amino acids. A second group consumed a diet based on the food guide pyramid, which contained higher amounts of carbohydrates.

Both groups consumed the same number of calories, but the first group substituted high-quality protein foods, such as meats, dairy, eggs, and nuts, for foods high in carbohydrates, such as breads, rice, cereal, pasta, and potatoes. "Both diets work because, when you restrict calories, you lose weight. But the people on the higher-protein diet lost more weight. Some people refer to this as the metabolic advantage of a protein-rich diet," said Layman.

The study included two levels of exercise. "For one group, we recommended that they add walking to their lives. They usually walked two to three times a week, less than 100 minutes of added exercise," the researcher said. The other group was required to engage in five 30-minute walking sessions and two 30-minute weightlifting sessions per week. In both groups of dieters, the required exercise program helped spare lean muscle tissue and target fat loss.

But, in the protein-rich, high-exercise group, Layman noted a statistically significant effect. That group lost even more weight, and almost 100 percent of the weight loss was fat, Layman said. In the high-carbohydrate, high-exercise group, as much as 25 to 30 percent of the weight lost was muscle.